I find this post very telling of how easily pop culture convices people that something is normative. I realize I am the antithesis to this thread, having not had my first alcoholic beverage until I was 24 (outside of religious practice), but despite my utter lack of interest I can safely say I dont know too many people who were "regular drinkers" until they were already, or cusping upon, the 21-year mark. I knew some, but they werent the majority. The same rang true for smoking. I only know a few people who were smokers/chewers before the age of 18, and most have already kicked the habit by now.
I think too many people are obsessed with flirting with the boundries of bad behavior to prove they are "adults" when such pretences show only the opposite to be true.
Please note I am not referring to legal drinking as bad behavior (if done responsibly), merely the drive of the young and stupid to rush into drinking instead waiting like responsible people.
As a further note I do recognize the legality of minors drinking in thier own homes under supervision of parents or legal guardians...but that is a fine line to walk and I personally wouldnt permit it, but that is one man's opinion.